Electrical Explosion Of Conductors Research Articles

Synthesis of Carbon Nanostructures on Nickel Nanopowders Produced by the Method of Electric Explosion of Conductors

The authors present the results of experiments on the synthesis of carbon nanostructures by the method of thermal chemical gas-phase deposition with the use of nickel nanopowders produced by the method of electric explosion of conductors and utilized as the catalysts. To study the process of origination and growth of individual carbon nanostructures, the authors conducted experiments not only on nanopowders, but also on separated clusters. Experiments were conducted at different temperatures (200–700°C) and pressures (100–400 mbar) to determine optimum conditions and the lower temperature boundary for carbon-nanostructure synthesis. The experiments have shown that the lower boundary of synthesis for nanopowders is a temperature of 325°C. For the separated powders, as for the nanopowders, stable growth of carbon nanostructures was observed at 350°C, but at pressures lower than 300 mbar. Unlike the carbon nanostructures produced on nanopowders, carbon nanostructures on separated powders exhibit a strong dependence of their origination and growth on temperature and pressure. Results of the Raman spectroscopy and of the x-ray structural analysis have shown that carbon nanostructures grown at 325°C and 300 mbar have the highest purity.

Magnetohydrodynamic perturbations arising in metallic conductors under the action of the discharge current

The presence of radial and axial mechanical perturbations in metallic conductors (cylinders and flat plates) arising under the action of a nanosecond discharge current are proved experimentally. The amplitude of the mechanical perturbations in solid-state conductors oscillates. The radial component of the mechanical perturbation should be considered as a reason for a magnetohydrodynamic instability with mode m = 0 and, accordingly, for the formation of strata at the electrical explosion of the conductor. Data for the electrical explosion of the metallic cylindrical conductor and flat metal sheet (foil) are presented.

Plating by electric explosion of conductors

The influence of the energy characteristics of the electric explosion of metal conductors on the structure and stability of a coating applied on a substrate has been studied experimentally. It is established that, at ω = ωc, the nickel coating consists of chaotically placed hardened metal drops and is unsteady. The coating formed by fine-dispersed nickel particles deposited from the gaseous phase in the course of an electroexplosion at ω = 2ωc is uniform and resistant to mechanical impacts.

Metastable states and their disintegration at pulse liquid heating and electrical explosion of conductors

The regularities of formation of metastable states and their disintegration under pulse liquid heating and electrical heating and explosion of conductors are studied. With a high energy flux density, the phase transitions occur with a high intensity of heat and mass fluxes, leading to spontaneous generation of a new phase and to phase explosion. The basic features of bubble-like disintegration in not uniformly superheated water and alcohol layers on the microheater are found. Regularities of matter disintegration with electrically exploded conductors are obtained. The metastable liquid disintegration is experimentally investigated for characteristic times of matter transfer to a metastable state of 1 to 4 µs; phase transitions during electric conductor explosion are studied at characteristic times of transfer to a metastable state to 200 ns. A common approach to describing the effects with radically different characteristic times of transfer of the matter to a metastable state is developed.

Fundamental aspects of oxidation of electroexplosive nickel nanopowder

Fundamental aspects of the process in which a nickel nanopowder produced by an electric explosion of conductors is oxidized under heating in air at a linearly increasing temperature and in the isothermal mode were studied. It is shown that the dispersion composition of the powder, structure of the metallic core of nickel particles, and characteristics of the oxide shell affect the kinetic parameters of the process. An explanation is suggested for specific features of the macrokinetic reaction mode caused by the joint influence exerted by the relative amounts of fractions of different-size particles in the powder and by the characteristic of the oxide layer. The reaction kinetics is simulated, with the size distribution function of nickel particles taken into account.

Characteristics of nanopowders produced by electrical explosion of tin-lead alloy conductors in air

The article discusses the investigations into the phase and chemical composition of nanopowders produced upon electrical explosion of conductors made of tin-lead alloy (POS-61) in air. It is demonstrated that, in the course of electrical explosion and subsequent cooling of the dispersion products, there occurs a slight enrichment (by 3–6 at %) of the surface and subsurface layers of the powder particles with lead in comparison with its content in the initial alloy.

Thermodynamics of phase transitions in liquids in external fields

We examine the conditions of phase equilibrium and transformations in a liquid located in an inhomogeneous external potential force field. If the force acting on the mass unit depends on the phase state, then a field-induced shift in phase equilibrium arises. As a result, at the phase interface at equal temperatures, the chemical potentials of the substance of phases do not coincide, although the full chemical potential is constant over the system. As well, one of the phases is located in a state which, in the absence of field, would be metastable. Such a field-induced phase equilibrium becomes impossible when one of the phases reaches the limiting state (spinodal). In this case, the system passes jumpwise into a new disperse state. We show that the above-mentioned features of phase equilibria in liquids and external fields manifest themselves in various physical systems and processes. These are electrical explosion of conductors, electrical explosion of micropoints on a cathode surface, and destruction of the surface of dielectrics by fast multicharged ions. Electric field also fosters the formation of nuclei of the competing phase in a supersaturated vapor and facilitates boiling of liquids on inhomogeneous heated surfaces. We discuss the possibility of achieving unusual states of substances, such as deeply supercooled hydrogen and ice at room temperature under the action of external fields.

Excess energy in the electroexplosive nanopowders

The electroexplosive route for nanopowders production is a rapidly occurring nonequilibrium process under the action of high power density energy. The electrical explosion of conductor (EEC) powder particles have a spherical shape with protective oxide–hydroxide layer which is an adsorbed layer of working gas on the surface of particles. The formation of EEC end products (nanopowder) occurs in conditions of coexistence of metal in different states: the vapor form (cluster), plasma and superheated liquid. In this work, the formation of particles and excess energy stored during EEC were studied. Themal analysis is suggested as a method for the determination of excess energy value. According to the results of the thermal analysis, the excess energy value for nanosized aluminum powder with various storage time after passivation are 61.99–11.89 kJ/mole, respectively.

Deformation behaviors of a TiZrNiCuBe bulk metallic glass under shock loading

In the present work, the shock responses of Ti 40Zr 25Ni 3Cu 12Be 20 bulk metallic glass (BMG) were investigated by using a planar impact technique on an electrical explosion of conductor (EEC) installation. The spallation occurs even if the stress behind the shock front is less than the Hogoniot elastic limit (HEL) stress of the Ti-based BMG. When the velocity of aluminum flyer with thickness of 1.7 mm is 570 m/s, the spall strength of the alloy sample is 2.9 GPa while the stress, strain and particle velocity behind the shock front are 4.3 GPa, 2.8% and 150 m/s, respectively. The calculated yield strength for the alloy upon the dynamic loading is much larger than that under the quasistatic compressive loading. The scanning electron microscope (SEM) observation indicates that, after dynamic loading, the free surface of the sample forms a lot of shear bands and cracks. Optical microscope (OM) shows that cracks and microvoids, which cause the occurrence of the spallation of the sample, are distributed on the cross-section of the recovered Ti-based BMG sample.

Nanosized structure formation in metals under the action of pulsed electric-explosion-induced plasma jets

A new mechanism is proposed that explains the formation of a thin nanostructural near-surface layer in the alloyed zone formed during the metal surface fusion treatment under the action of a pulsed plasma jet generated by the electric explosion of conductors. The proposed mechanism is based upon the development of the Kelvin-Helmholtz (KH) instability at the plasma-melt interface. A dispersion equation is obtained for the KH problem with allowance for the viscous and capillary stresses in the melt. The dependence of the KH instability increment on the surface perturbation wavelength exhibits a maximum in a nanometer range for the relative velocities of plasma with respect to the melt (within 100–1000 m/s) achieved under real treatment conditions.

Mechanisms of metallic nanoparticle generation during an electric explosion of conductors

The mechanisms of conductor fracture and the generation of metallic nanoparticles during an electric explosion are discussed. The fracture of polycrystalline conductors with a crystallite size smaller than 100 nm during rapid introduction of energy is shown to occur due to its localization at grain boundaries. The dynamics of the explosion products (droplets, vapor) flying into a buffer gas is numerically simulated in terms of the mechanics of heterogeneous media with allowance for condensation and evaporation. The calculated size distributions of particles agree with the experimental distributions both qualitatively and quantitatively.

Obtaining ultrafine metal powders under electric explosion of conductors in liquid: Part III. The optimum mode for explosion of conductors in gases; Comparison with explosion in liquid

The electric explosion of nickel-containing conductors is experimentally studied for the optimum mode in air. The results of explosion of conductors in air and in water are compared. It is shown that explosion in air of conductors completely identical to those exploded in water leads to a change in the discharge duty. The conditions required for the optimum mode of explosion of conductors in air are determined.

Investigations on optimal mode of electric explosion of conductors in water and air

In this work, it is established that the ratio of the stored energy to the conductor weight W0/m can be used as a similarity criterion for the electrical characteristics of conductor explosion. It is shown that the specific stored energy W0/m and the ratio of the sublimation energy of the conductor metal to the stored energy Ws/W0 for the optimal modes of electric explosion of conductors in air do not depend on externally driven parameters in the same way as for an explosion in water. The conditions providing a high rate of energy release in a discharge gap during EEC in air are determined. The relation between the optimal parameters of conductor explosion in water and air is found.

Oxidation of copper nanopowders on heating in air

The morphology and structure of copper nanopowders produced by electrical explosion of conductors are considered. The regularities of nanopowder oxidation in air were studied during linear and isothermal heating. The characteristics of initial powders in relation to the kinetic oxidation parameters were determined and the dependence of phase composition of the products of nanopowder oxidation on the heating conditions and dispersity of initial powders was found.

On obtaining of ultrafine metal powders under electric explosion of conductors in a liquid. Part II: The optimum mode for the explosion of conductors in a liquid

The electric explosion of different metallic conductors in a liquid in the optimum mode has been experimentally studied. The conditions for the implementation of the optimum mode of the conductor explosion, when all the energy stored in the capacitor is injected into the conductor in the course of the first half-period of the discharge, have been determined. It has been found that the specific energy injected into the conductor in the optimum mode does not depend on the conductor sizes and circuit parameters. A correlation showing what amount of energy can be injected into the conductor in the process of its explosion in the optimum mode has been obtained. It has been shown that the size of the particles obtained in the process of the conductor explosion in the optimum mode only depends on the properties of the metal.

Structure and texture of oxyhydroxides formed by oxidation of nanodispersed aluminum with water

Aluminum oxyhydroxides were prepared by oxidation with water (55°C) of nanodispersed aluminum powders obtained by electric explosion of conductors in argon, nitrogen, carbon dioxide, and their mixtures. The structure and texture of aluminum oxyhydroxides were studied using methods of thermal desorption of nitrogen, derivatography, electron microscopy, and X-ray phase analysis.

On obtaining of ultrafine metal powders at electric explosion of conductors in liquid Part I. Peculiarities of explosion of conductors in liquid

The features of electric explosion and dispersion in a liquid of metallic conductors with their thermodynamic and electric parameters differing over a wide range were investigated. The experimental data analysis allowed selecting three pairs of metals being the closest in the obtained parameters of the explosion. It is obvious that the size of the obtained particles depends on the density of the energy injected into the conductor mass unit by the moment of explosion. A reverse dependence between the energy of the arc stage of the explosion and the size of the particles is found. The distribution of the obtained particles by size is more homogeneous than at the explosion of conductors in gases.

Electrical explosion of conductors in the high-pressure zone of a convergent shock wave

The effect of the environmental pressure on the electrical explosion of a conductor (fine tungsten wire of diameter 30 μm) in an insulating liquid (distilled water) is studied. The pressure in the water is produced by exploding a multiwire array with the test conductor on its axis. Along with the experiment, the magnetohydrodynamic simulation of the explosion is carried out. It is shown that a high pressure produced in the explosion zone retards the electrical explosion of the conductor and, consequently, increases the explosion energy.

Phase composition and defect substructure of nickel alloyed with boron and copper by electric explosion of conductors

Using methods of electron microscopy, we have discovered that combined electroexplosive alloying of nickel with boron and copper gives rise to a multilayer structure. An outer amorphous crystalline layer incorporating 2–3 nm nickel-and copper-boride, oxide, and boride-oxide crystallites is formed on the alloyed surface. The intermediate (subsurface) layer 1–2 µm thick is made up of NiB12 and Ni4B3 crystallites 120–130 nm in size, with boron-and copper-oxide particles observed along the grain boundaries. The underlying thick layer exhibits a cellular Ni-Cu-B melt crystallization structure grading initially into a high-rate dendritic crystallization structure and then into a granular structure. The electroexplosive alloying process is found to bring into existence a high scalar dislocation-density substructure in nickel crystallites both in the alloyed zone and in the adjacent heat-affected zone.

High-energy radiation generated during electric explosion of a conductor in a longitudinal magnetic field

Our recent experiments [1] with the electric explosion of conductors in vacuum with an applied strong longitudinal magnetic field showed that this process was accompanied by radiation capable of penetrating through metal layers of considerable thickness. The high intensity of this radiation allowed it to be reliably detected outside the vacuum chamber using a photographic film with an amplifying luminescent (ZnS) screen situated in a paper envelope at a distance above 3 m from the region of explosion. In the same series of experiments, it was established that elements of the setup situated in the vicinity of the explosion exhibited residual radioactivity. This radioactivity was manifested, in particular, by flare spots on a photographic film in contact with an amplifying phosphor screen contained in a paper cassette that was placed inside the solenoid gap upon the discharge. No such explosion-induced radioactivity was observed in analogous experiments performed without an applied magnetic field. This paper presents the first results of investigations of the induced radioactivity, in which the activation detector was a gold ring situated at a distance of about 0.2 m from the axis of the exploding conductor.